1. Field of the Invention
The present invention relates to a prismatic sealed battery module, and more particularly to a prismatic sealed battery module which succeeds in reducing connection resistance with respect to an external terminal.
2. Description of Related Art
A conventional rechargeable battery module is typically composed of a plurality of cells connected together to obtain a desired electric power capacity. Such a rechargeable battery module is constructed by stackingly arranging a plurality of prismatic cells such that longer side surfaces of battery cases are arranged opposite each other, followed by placing an end plate outside the battery case of each endmost cell, further followed by binding them together with a tie band. In the rechargeable battery module, each of the cells is connected, via a lead extended upward from an upper end of its electrode plate, to an external terminal attached to a cover of the battery case. Then, the external terminals are connected with each other by connection plates, thus effecting interconnection between the cells.
In this conventional construction, due to the complexity of interconnection between the cells, a large number of constitution parts are required. Moreover, the connection paths between the cells are long and the connection points are large in number. This leads to an undesirable increase in the cost. In addition, occurrence of unduly large part resistance makes it difficult to improve power output and service life characteristics in the rechargeable battery module.
In light of the foregoing, the present applicant has previously proposed a prismatic sealed battery module 101 shown in FIG. 5 that incorporates a plurality of cells 102. In the figure, the reference numeral 103 denotes a prismatic battery case. The prismatic battery case 103 is formed in the shape of a flat prism by integrally and contiguously arranging prismatic battery cases 104 of the cells 102 with a shorter side surface and a longer side surface, each of whose shorter side surfaces is common to adjacent such battery cases as a partition wall 105. Upper openings of the battery cases 104 are sealed with an integrally-formed cover 106. Connection holes 107 are formed outside the shorter side surface of each endmost battery case 104 and in the upper part of the partition wall 105 between adjacent battery cases 104.
The battery cases 104 each accommodate an electrolyte and an electrode plate group 108 formed by layering rectangular positive and negative electrode plates with a separator interposed therebetween. Thereby, the cell 102 is realized. Part of the positive and negative electrode plates of the electrode plate group 108 extend sideways in mutually different directions, so as to form leads 109a and 109b. The leads 109a and 109b of the positive and negative electrode plates have their edges connected to collector plates 110a and 110b, respectively, by welding or other means.
At an upper part of the collector plate 110a, 110b is protrudingly formed a connecting projection 111 which is fitted in the connection hole 107. Interconnection between adjacent battery cases 104 is effected by connecting together the connecting projections 111 of the positive/negative collector plates 110a and 110b by welding. Fitted in the connection hole 107 formed on the outer shorter side surface of the endmost battery case 104 is a positive or negative external terminal 112, whose connecting projection 113 is connected to the connecting projection 111 of the collector plate 110a or 110b by welding. In this way, a plurality of the cells 102 accommodated in the prismatic battery case 103 are connected in series with each other, so that power output is produced between the endmost external terminals 112.
However, the construction shown in FIG. 5 has the following disadvantage. Although a current-carrying path from the positive or negative electrode plate, through its respective lead 109a or 109b, to the collector plate 110a or 110b can be made short, in order to complete the current-carrying path between the collector plate and the external terminal 112, current must take a path reaching the upper end of the collector plate 110a, 110b first, and then pass through a welding point between the two front ends of the connecting projection 111 of the upper end and the connecting projection 113 of the external terminal 112. Consequently, the length of the entire current-carrying path becomes unduly long, and also the connection resistance is increased because of the necessity of energizing a portion having a small sectional area, giving rise to a-great loss induced by electrical connection resistance.
Another problems with the construction are that: since interconnection between the cells 102 is effected by weld-connecting together the front ends of the connecting projections 111 respectively formed at the upper ends of the collector plates 110a and 110b, the connection path must be made to take a detour, resulting in an increase in the length of the connection path; since the weld-connection is made only at one point, the resistance is increased; using the collector plates 110a and 110b leads to an increase in the cost; and the collector plates 110a and 110b are arranged on both sides of the electrode plate group 108, and their upper parts need to be so formed as to extend beyond the upper end of the electrode plate group 108, resulting in an increase in the volume of the battery case 104.